Crawler tractor

ABSTRACT

The purpose of the invention is to enable a crawler tractor to brake and stop certainly without applying a load to an engine and a driving mechanism, and without complicated operation. An operation link links a conic linkage ( 53 ) which links a steering wheel ( 7 ) with a main speed change lever ( 55 ) of the crawler tractor, and with an operation mechanism of a brake pedal ( 54 ). A neutral return mechanism for the operation link is provided. The operation link neutral return mechanism comprises a hook-like cam lever ( 61 ). When the brake pedal is depressed, the main speed change lever is moved to its neutral position before braking force occurs, and then, the brake is actuated. Accordingly, engine brake is used effectively, and the brake can be miniaturized.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a crawler tractor used for agriculturalwork and the like. More particularly, it relates to a driving mechanism,an HST and a brake mechanism concerning speed change, traveling andsteering of the crawler tractor.

2. Related Art

Conventionally, there is a well-known agricultural working vehicle(crawler tractor) provided with a hydraulic stepless transmission fortraveling and a hydraulic stepless transmission for turning as onetypical hydraulic-driving agricultural working machine having left andright independent crawler type traveling devices.

It is important for improving operativity of the crawler tractor toensure transmission/isolation of driving force and braking. Therefore, acrawler tractor is provided with a neutral-position holding mechanismfor ensuring neutral location of the HST for traveling and the HST forturning.

As described in the Japanese Patent Laid Open Gazette Hei. 8-242601, forenhancing certainty of cutting off transmission of driving force tocrawler traveling devices at the time of stopping the vehicle, withrespect to some crawler tractors, an additional clutch device isdisposed on a driving power train and a hydraulic circuit is providedfor controlling the clutches. With respect to other crawler tractors, aneutral return mechanism for a steering device is disposed in thevicinity of the HST for turning and a steering shaft connected to thesteering device is connected to the HST for turning through an universaljoint or the like so as to transmit steering operation.

With regard to the above-mentioned hydraulic circuit, there is a crawlertractor constructed such that an oil cooler for cooling pressure oilsupplied into a transmission casing is disposed in front of a radiatorand the oil cooler is cooled by cooling wind generated from a fan drivenby an engine. Also, as shown in the Japanese Patent Laid Open GazetteHei. 10-54462, there is a crawler tractor such that pressure oilsupplied from a charge pump is cooled by an oil cooler and then thefluid is supplied to each HST.

As disclosed in the Japanese Patent Laid Open Gazette Hei. 8-280206, forexample, there is a well-known construction for connecting a sub controlvalve for controlling a working machine connected to a crawler tractor,wherein the sub control valve is detachable, and when the sub controlvalve is attached, hydraulic ports are connected with respective portsof the sub control valve through hydraulic pipings, and when the subcontrol valve is not attached, metal is disposed so as to cover an uppersurface of a cylinder casing and the ports are connected mutuallythrough oil passages provided within the metal.

However, with regard to many of the conventional crawler tractors, aninscribed gear is used as one of gears constituting a planetary gearingof a differential mechanism for independent left and right crawler typetraveling devices. Accordingly, the planetary gearing becomesdiametrically large.

Besides, for providing a steering brake to the left and right axles,left and right brake mechanisms are required, and they are large-sizedso as to brake a large torque. Such a mechanism results in not onlyrestriction of design of the crawler tractor but also increase of fulllength of a linkage, thereby hindering improvement of operativity at thetime of braking.

Furthermore, conventional mechanisms for holding the HST for travelingand the HST for turning in neutral and a conventional mechanism forholding a steering device in neutral are complicated in construction andrequire much effort for assembling thereof and the like, therebyhindering reduction of costs for their production.

Besides, a conventional main circuit of the HST for traveling is notprovided with a valve for releasing pressure from the HST for traveling.Accordingly, pressure is accumulated in the HST for traveling, therebymaking an output shaft hard to rotate, requiring a large power forstarting thereof, and hindering smooth change of speed or gears.

With regard to cooling of pressure oil, if an oil cooler for coolingpressure oil used for a transmission is disposed alongside of acapacitor for an air-conditioner and a radiator of an engine, coolingefficiency may fall. Furthermore, maintenance work may becomecomplicated.

With regard to the conventional construction of hydraulic piping, ittakes a long time for attaching the piping. Every when the oil pressureis selectively extracted to either front or rear side, it is necessaryto close hydraulic ports on an unused side.

SUMMARY OF THE INVENTION

In a crawler tractor according to the invention, power from an engine istransmitted into a transmission casing disposed at a rear portion of thevehicle body and varied in speed, and a traveling power take-off sectiontransmits the speed-varied power to a traveling device. The travelingpower take-off section is disposed in a lower portion of thetransmission casing, and a brake mechanism is provided in the travelingpower take-off section. Accordingly, a space in the transmission casingcan be used effectively. Furthermore, the brake mechanism is disposednear a brake pedal.

In a crawler tractor according to the invention, power from an engine istransmitted into a transmission casing through a hydrostatic steplesstransmission for traveling, and a traveling power take-off sectiontransmits the power varied in speed in the transmission casing to atraveling device. When a brake pedal is depressed, a swash plate of thehydrostatic stepless transmission for traveling returns to a neutralposition and then a parking brake provided in the traveling powertake-off section is actuated. Accordingly, the capacity of the brake maybe small and the brake device may be compacted.

In a crawler tractor disposed in a crawler tractor according to theinvention, power from an engine is transmitted to a sub transmission ina transmission casing, and a traveling power take-off section transmitspower to a traveling device. A braking device is provided in thetraveling power take-off section in a lower portion of the transmissioncasing and in the vicinity of the sub transmission. Therefore, a linkagebetween the brake device and the transmission can be simplified.

According to the invention, a conic linkage links a steering device witha main speed change lever, and an operation link is provided forconnecting a brake pedal operation mechanism with the conic linkage. Theoperation link is provided with a neutral return mechanism, which isdisposed in a lower portion of a section incorporating the coniclinkage. The neutral return mechanism is disposed on the way of thelinkage connecting the main speed change lever with the steering wheel,thereby being simplified. A play of the linkage is equally sharedbetween the main speed change lever and the steering wheel so as toimprove their operativity.

According to the invention, a conic linkage links a steering device witha main speed change lever, an operation link is provided for connectinga brake pedal operation mechanism with the conic linkage, and a neutralreturn mechanism for the operation link is provided in the operationlink. The neutral return mechanism for the operation link comprises ahook-like cam. Accordingly, the neutral return mechanism is simplifiedand facilitates for easy adjustment of the neutral return mechanism.Such a simple and easy neutral return mechanism improves operativity anddurability thereof.

According to the invention, a conic linkage links a steering device witha main speed change lever, an operation link is provided for connectinga brake pedal operation mechanism with the conic linkage, and a neutralreturn mechanism for the operation link is provided in the operationlink. A hook-like cam is arranged on the way of a link between the coniclinkage and the main speed change lever. Therefore, a play of thelinkage is not disposed eccentrically, thereby reducing an error in amechanism for operation thereof.

According to the invention, a conic linkage links a steering device witha main speed change lever, an operation link is provided for connectinga brake pedal operation mechanism with the conic linkage, and a neutralreturn mechanism for the operation link is provided in the operationlink. When an operation for braking is performed, a brake begins to workafter a swash plate control arm of an HST is positioned in the vicinityof its neutral position. Therefore, when the brake operation isperformed, a brake caused by the HST is applied and then a brake isactuated so as to stop. Accordingly, the vehicle is always braked whenthe brake operation is performed. The time lug between the two brakesystems improves a feeling of braking operation.

According to the invention, an operation link links a main speed leveroperation mechanism with a brake pedal operation mechanism, and aneutral return mechanism for the operation link is provided in theoperation link. A servo valve is disposed between the brake pedaloperation mechanism and a swash plate control arm of an HST. Operationof the brake pedal is transmitted to the swash plate control arm of aHST through the servo valve tardily. Therefore, the feeling in operationis improved and a hard brake is prevented.

According to the invention, in a steering mechanism, a conic linkagelinks a steering device with a main speed change lever, and a rotationrestriction cam is provided in a lower portion of a steering shaftconnected to a steering wheel. The cam is provided with a portion forabutting against a neutral-returning member and with a portion forabutting against a rotation-restricting stopper. Therefore, a space inan upper portion of a steering column is efficiently usable.

According to the invention, in a steering mechanism, a conic linkagelinks a steering device with a main speed change lever, and a cam isformed to gradually expand in its radial direction as the cam goes apartfrom a neutral position thereof. The cam is provided at an end thereofwith a portion for abutting against a stopper for restriction ofrotation. Therefore, a mechanism for neutral-returning of the steeringdevice is simplified, and the cam is also simplified.

According to the invention, a steering mechanism comprises a coniclinkage linking a steering device with a main speed change lever. Astopper and a neutral-returning member arranged symmetrically withrespect to an axial center of a cam. Therefore, the single stopper isprovided to the cam so as easily to restrict rotational degree of thecam. Also, the mechanism for restricting rotation of the cam is enhancedin durability.

In a crawler tractor according to the invention, power form an engine istransmitted to an HST for traveling and speed change operation is doneby the HST for traveling. A mechanism for releasing residual pressurecomprises a valve for releasing residual pressure which is provided to amain circuit of the HST for traveling. Accordingly, pressure is releasedfrom the HST for traveling so as to facilitate easy actuation of anoutput shaft for traveling and easy restart of an engine. Also, the gearchange of a sub transmission is done smoothly.

In a crawler tractor according to the invention, power form an engine istransmitted to an HST for traveling and speed change operation is doneby the HST for traveling. A mechanism for releasing residual pressurecomprises a valve for releasing residual pressure which is provided to amain circuit of the HST for traveling. The valve for releasing residualpressure is interlockingly connected with a brake pedal. Therefore, anengine is easily started and load applied on the engine and a drivemechanism is lightened.

In a crawler tractor according to the invention, power form an engine istransmitted to an HST for traveling and speed change operation is doneby the HST for traveling. A mechanism for releasing residual pressurecomprises a valve for releasing residual pressure which is provided to amain circuit of the HST for traveling. The valve for releasing residualpressure is an electro-magnetic valve linked with a key switch.Accordingly, an additional operation for releasing the residual pressureis unnecessary. When the starter actuates, pressure in the HST is alwayslow so as to improve the start of the engine.

In a crawler tractor according to the invention, power form an engine istransmitted to an HST for traveling, speed change operation is done bythe HST for traveling, the power from the engine is also transmitted toan HST for turning, and steering operation is done by transmittingoutput of the HST for turning to a differential mechanism. A clutch isdisposed between the HST for turning and a transmission shaft fortransmitting driving force to the differential mechanism. Such a simpleconstruction is provided for shutting off driving force from the HST forturning. Therefore, loss of driving force at the time of stopping thevehicle can be reduced, thereby improving fuel economy of the crawlertractor.

In a crawler tractor according to the invention, power form an engine istransmitted to an HST for traveling, speed change operation is done bythe HST for traveling, the power from the engine is also transmitted toan HST for turning, and steering operation is done by transmittingoutput of the HST for turning to a differential mechanism. An inputshaft of the HST for turning projects from a casing of the HST forturning, and a pulley is equipped on the input shaft. By such a simpleconstruction, a PTO section is provided at a front portion of thevehicle body. Therefore, manufacturing costs is reduced, and the PTOsection is compacted, so as to improve the flexibility of design.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective front view of a crawler tractor;

FIG. 2 is an entire side view of the crawler tractor;

FIG. 3 is a side view showing arrangement of an engine, HSTs and atransmission casing;

FIG. 4 is a sectional side view showing a construction of the reartransmission casing;

FIG. 5 is a sectional side view showing a construction of a brakemechanism;

FIG. 6 is a sectional plan view showing the construction of the brakemechanism;

FIG. 7 is a side view showing a frame construction of the crawlertractor;

FIG. 8 is a plan view showing the frame construction of the crawlertractor;

FIG. 9 is a side view showing a connection construction of the engineand the rear transmission casing;

FIG. 10 is a front view showing the connection construction of theengine and the rear transmission casing;

FIG. 11 is a front view showing a construction of the rear transmissioncasing and a connection frame;

FIG. 12 is a plan view showing another frame construction of the crawlertractor;

FIG. 13 is a front view showing a connection construction of theconnection frame and a center support frame;

FIG. 14 is a plan view showing a construction of an attaching linkage;

FIG. 15 is a side view showing the construction of the attachinglinkage;

FIG. 16 is a side view showing an anchored state of a top link;

FIG. 17 is a side view showing a construction of hydraulic piping from asub control valve;

FIG. 18 is a plan view showing the construction of hydraulic piping fromthe sub control valve;

FIG. 19 is a schematic diagram showing a connection construction of thesub control valve;

FIG. 20 is a schematic diagram showing a construction of electromagneticswitching valves;

FIG. 21 is a rear view showing an arrangement of a fuel tank and apressure oil tank;

FIG. 22 is a plan view showing the arrangement of the fuel tank and thepressure oil tank;

FIG. 23 is a side view showing a construction of an auxiliary basedisposed in the vicinity of the fuel tank;

FIG. 24 is a bottom view showing a construction of the auxiliary base;

FIG. 25 is a drawing showing a construction of a hydraulic circuit;

FIG. 26 is a side view showing a construction of hydraulic piping;

FIG. 27 is a plan view showing the construction of the hydraulic piping;

FIG. 28 is a side view showing an arrangement of a capacitor forair-conditioner and a radiator;

FIG. 29 is a sectional plan view showing a construction of a sealmember;

FIG. 30 is a side view showing an arrangement of an oil cooler and thepressure oil tank;

FIG. 31 is a plan view showing another embodiment about arrangement ofthe oil cooler;

FIG. 32 is a side view showing a construction of a front part of thecrawler tractor;

FIG. 33 is a sectional side view showing a construction of a HST forturning;

FIG. 34 is a sectional side view showing a construction between the HSTfor turning and a differential mechanism;

FIG. 35 is a plan view showing a construction of the HST for turning;

FIG. 36 is a side view showing a construction of a front PTO section;

FIG. 37 is a side view showing control devices of the crawler tractor;

FIG. 38 is a side view showing a construction of a conic linkage;

FIG. 39 is a sectional rear view showing a construction of the coniclinkage;

FIG. 40 is a side view showing an actuation construction of a main speedchange lever;

FIG. 41 is a side view showing an actuation construction of a brakepedal;

FIG. 42 is a front view showing the actuation construction of the brakepedal;

FIG. 43 is a drawing showing an interlocking construction of the brakepedal and the main speed change lever;

FIG. 44 is a side view showing a construction of the brake pedal and acam lever;

FIG. 45 is a side view showing a construction of a rod connected to thebrake mechanism;

FIG. 46 is a schematic diagram showing a brake mechanism using a servovalve;

FIG. 47 is a front view showing a construction of a steering box;

FIG. 48 is a sectional side view showing a construction of the steeringbox;

FIG. 49 is a plan view showing a construction of a neutral returnmechanism of steering;

FIG. 50 is a plan view showing a construction of a switch disposed in acam box;

FIG. 51 is a side view showing an arrangement of a residual pressurerelease valve;

FIG. 52 is a hydraulic circuit diagram showing a connection constructionof the residual pressure release valve;

FIG. 53 is a schematic diagram showing an example of the actuationconstruction of the residual pressure release valve;

FIG. 54 is a schematic diagram showing a construction of the residualpressure release valve;

FIG. 55 is a sectional plan view showing a construction of thedifferential mechanism, and

FIG. 56 is a schematic diagram showing rotation action of a pressureplate.

DETAILED DESCRIPTION OF THE INVENTION

Best Mode for Carrying out the Invention

The invention will be described in detail according to attacheddrawings.

First, description will be given of a general construction of a crawlertractor as an embodiment having a steering device according to theinvention.

As shown in FIGS. 1 and 2, an engine 3 is arranged above front portionsof crawler type traveling devices 1. A rear transmission casing 5 isarranged above rear portions of the device 1. The engine 3 is coveredwith a bonnet 4 and fixed at a lower portion thereof between left andright main frames 6.

A steering column 2 is disposed behind the bonnet 4, and a steeringwheel 7 is arranged above the steering column 2. A seat 8 is disposedbehind the steering wheel 7, and a step 18 is arranged between lowerportions of the steering column 2 and the seat 8, thereby constructing adriver's compartment, which is covered with a cabin 9.

The vehicle is provided at the rear end thereof with a three pointlinkage 10 for supporting various kinds of work machines.

The crawler type traveling devices 1 are supported by respective crawlerframes 15. The crawler frames 15 have front end portions, to which afront transmission casing 16 supporting driving sprockets 11 is fixed.Each crawler frame 15 rotatably supports an idler 12 at a rear endportion thereof, and rollers 13 between the drive sprocket 11 and theidler 12. A crawler belt 14 is looped over the drive sprocket 11, theidler 12 and the rollers 13.

Description will now be given of a power transmission system of thecrawler tractor in accordance with FIGS. 3 and 4.

A clutch casing 19 is attached to the rear portion of the engine 3. Adamped output shaft 42 is extended rearward from the clutch casing 19and connected to an input shaft of a hydraulic stepless transmission fortraveling (hereafter, referred to as an HST for traveling) 22 attachedto the front portion of the rear transmission casing 5.

The rear transmission casing 5 contains a sub transmission 41, a PTOtransmission 43 and others. Driving force from the HST for traveling 22is transmitted to the sub transmission 41. The PTO transmission 43 isconnected to the input shaft of the traveling HST 22 through a clutch44. A lower front portion of the rear transmission casing 5 serves as atraveling power take-off section in which an output shaft 102 isdisposed.

In front of the engine 3 is disposed the front transmission casing 16having a hydraulic stepless transmission for turning (hereafter,referred to as an HST for turning) 20 attached to the front surfacethereof. The front transmission casing 16 is supported by the frontportion of the main frames 6 so as to be arranged in the front portionof the vehicle body.

The HST for turning 20 is driven by driving force from the engine 3. Thedrive sprockets 11 are driven by resultant output force of output forcefrom the HST for turning 20 and output force from the above-mentionedsub transmission 41.

The output rotation of the HST for traveling 22 on its motor side isvaried by the sub transmission 41, and then inputted to a differentialgearing through a transmission shaft 45.

The differential gearing will now be described in accordance with FIG.55.

In the rear transmission casing 5, the output shaft 102 transmits powerfrom the engine 3 through a universal joint and the transmission shaft45 to an input shaft 319 of the differential gearing in a differentialcasing 330. Driving force of the input shaft 319 is transferred to aninput shaft 343 through bevel gears 341 and 342.

The rotational output of the output shaft 343 is divided into left andright planetary gear mechanisms 340L and 340R constituting thedifferential gearing. The left and right planetary gear mechanisms 340Land 340R comprise sun gears 344L and 344R, planetary gears 345L and345R, carriers 346L, 346R, 348L and 348R, output gears 347L and 347R,etc.

The rotation of the input shaft 343 drives the sun gears 344L and 344Rfixed on the left and right ends of the input shaft 343 in the samedirection and at the same speed. Each of the planetary gears 345L isshaped into two gears 360L and 361L stuck to each other on a commonrotational axis. The planetary gears 345R are formed substantiallysimilarly with the planetary gears 345L. The gears 360L and 360R engagewith the respective sun gears 344L and 344R, and the gears 361L and 361Rwith the respective output gears 347L and 347R.

Each of the planetary gears 345L is rotatably supported at one endthereof by a carrier 346L rotatably provided on the input shaft 343, andat the other end thereof by a carrier 348L rotatably provided on a driveoutput shaft 349L. The planetary gears 345L are rotatably supportedbetween the carriers 346L and 348L, and revolved together with thecarriers 146L and 148L around the rotational axis of the input shaft 343and the drive output shafts 349L and 349R.

The assembly of planetary gears 345R is substantially similar with thatof planetary gears 345L.

A gear 362L is formed on the outer peripheral surface of the carrier346L and engages with a gear 354L. A divisional shaft 353L penetratesthe gear 354L at an intermediate portion thereof. A bevel gear 352L isfitted onto one end of the delivery shaft 353L and engages with a bevelgear 325 fitted on a differential transmission shaft 224.

Similarly with the carrier 346L, the carrier 346R is formed on the outerperipheral surface thereof with a gear 362R, which engages with a gear354R. A divisional shaft 353R penetrates the gear 354R at anintermediate portion thereof. A bevel gear 352R is fitted onto one endof the divisional shaft 353R and also engages with the bevel gear 325.

With regard to the above construction, it is assumed that the steeringwheel 7 is kept in its neutral position. In this case, the HST forturning 20 is stationary so that the bevel gear 325 fixed on thedifferential transmission shaft 224, and the bevel gears 352L and 352Rand the gears 354L and 354R fixed on the respective divisional shafts353L and 353R remain stationary, thereby braking the left and rightcarriers 346L and 346R engaging with the respective gears 354L and 354R.Accordingly, the carriers 146L and 146R remain substantially stationarywithout rotating around the input shaft 343.

In this situation, rotation of the sun gears 344L and 344R istransferred into the planetary gears 345L and 345R rotatably supportedon the stationary carriers 346L and 348L.

Therefore, the output gears 347L and 347R engaging with the gears 361Land 361R of the planetary gears 345L and 345R are rotated so as torotate the left and right drive output shafts 349L and 349R.

Namely, while the steering wheel 7 remains in its neutral position, thedifferential gearing receives driving force from the engine 3 throughonly the transmission casing 5 and the input shaft 319, thereby rotatingthe left and right drive output shafts 349L and 349R at the same speedin the same direction.

On the other hand, when the steering wheel 7 is rotated for turning ofthe vehicle, the differential transmission shaft 224 of the HST forturning 20 is rotated in correspondence to the rotational degree of thesteering wheel 7.

At this time, the bevel gear 325 is rotated so as to rotate the bevelgears 352L and 352R fixed on the divisional shafts 353L and 353R at thesame speed in opposite directions through the bevel gear 325.

Accordingly, the left and right carriers 3146L and 346R engaging withgears 354L and 354R are rotated on the outer periphery of the inputshaft 343 at the same speed in opposite directions. The planetary gears345L are rotated integrally with the carriers 346L and 348L, and theplanetary gears 345R integrally with the carriers 346R and 348R, so thatthe planetary gears 345L and 345R revolve around the input shaft 343 atthe same speed in opposite directions.

If either the planetary gears 345L or 345R are rotated so that theirrelative rotation to the corresponding carrier 346L or 346R is oppositeto their relative rotation to the input shaft 343, the sum of the tworelative rotational speeds results in the rotational speed of thecorresponding output gear 349L or 349R. If the two relative rotationsare performed in the same direction, the remainder of subtractionbetween the two relative rotational speeds results in the rotationalspeed of the corresponding output gear 349L or 349R.

Namely, the resultant output of output from the engine 3 through thetransmission casing 5 and output from the engine 3 through the HST forturning 20 causes a difference between the rotational speeds of the leftand right drive output shafts 349L and 349R, thereby generatingdifference of rotation between the drive sprockets 11 of the left andright crawler type traveling devices, whereby the traveling vehicleturns left or right.

With regard to the HST for traveling 22, an output shaft 101 of the HSTfor traveling 22 is driven by the rotation of the input shaft of the HSTfor traveling 22. The drive rate and rotational direction of the outputshaft 101 is controlled by controlling angle of a swash plate of ahydraulic pump of the input shaft side.

Driving force of the output shaft 101 is transferred to the subtransmission 41, varied in speed by the sub transmission 41, andtransferred to the output shaft 102 in the traveling power take-offsection. The above-mentioned transmission shaft 45 is connected to theoutput shaft 102 in the traveling power take-off section.

A brake mechanism 74 is constructed in the vicinity of the output shaft102 so as to brake the output shaft 102. The output shaft 102 isconnected to a sun gear for driving the drive sprockets 11 through thetransmission shaft 45. Braking the output shaft 102 results in brakingthe drive sprockets 11.

The lower portion of the transmission casing below the sub transmission41 therein serves as the power take-off section in which the brakemechanism 74 is provided. The HST for traveling 22 is arranged in frontof the sub transmission 41, and the brake mechanism 74 is disposed underthe HST for traveling 22.

The arrangement of the brake mechanism 74 serving as a parking brake inthe lower portion of the rear transmission casing 5 is available for thebrake mechanism 74 to approach a later-discussed brake pedal 54, so thata linkage, etc. therebetween becomes simple and it becomes so short asto reduce its friction loss and clearance, thereby facilitatingoperavility of the vehicle.

Furthermore, due to the structure peculiar to the crawler tractor, anadvantageously large space is reserved under the cabin between the HSTfor traveling 22 and the engine 3. Specifically, the space may be leftas it is so as to facilitate for maintenance. Otherwise, any additionalequipment such as a mechanism or a hydraulic valve for controlling aworking machine may be disposed in the space without changing theappearance of the vehicle.

Description will be given on the brake mechanism 74 in accordance withFIGS. 5, 6 and 56.

The output shaft 102 is rotatably held by a transmission casing 107 anda brake cover 108 through a bearing, and a gear 102 a is fixedly fittedon a rear end of the output shaft 102. The gear 102 a engages with agear of the sub transmission 41 so that driving force from the subtransmission 41 is transferred to the output shaft 102. The brake cover108 is arranged in front of the brake mechanism 74 and fitted to thetransmission casing 107 so as to cover the brake mechanism 74.

A pressure plate 103, and alternate multiple brake plates 105 andfriction plates 104 are arranged around the output shaft 102.

A front portion of the pressure plate 103 is fitted to an inside portionof the brake cover 108 so as to be restricted in its sliding directionby the brake cover 108. A spring 110, which is anchored at one of itsends to the brake cover 108, is connected to the pressure plate 103 soas to bias the pressure plate 103 forwardly.

A ball 109 is disposed between the pressure plate 103 and the brakecover 108, and engaged in a slot 103 b formed by the pressure plate 103and the brake cover 108.

In the pressure plate 13, the slot 103 b is formed like an arc centeredon the output shaft 102. The depth of the slot 103 b contacting with theball 109 is reduced according to rotation of the pressure plate 103.

Accordingly, as shown in FIG. 56, by depressing the later-discussedbrake pedal 54, the linkage mechanism is operated so that an actuationarm 113 is rotated centering around a steering input shaft 112projecting from the actuation arm 113. A notch is provided on an end ofthe steering input shaft 112. When viewed in the axial direction of thesteering input shaft 112, the notch is semicircular, and a contactsurface 112 a is formed as a chord of the semicircular shape so as toabut against a contact surface 103 a formed on the pressure plate 103.When the steering input shaft 112 is rotated, an edge of the contactsurface 112 a close to the output shaft 102 is moved downward so as topush down the contact surface 103 a of the pressure plate 103, therebyrotating the pressure plate 103 centering around the output shaft 102.Accordingly, the slot 103 b formed in the pressure plate 103 moves so asto gradually move the ball 109 from the deep portion to the shallowportion in the slot 103 b. The ball 109 is engaged in the slot 103 b soas not to move relative to the brake cover 108, and the pressure plate103 is slidable in the axial direction of the output shaft 102toward/away from the brake cover 108. As a result, the pressure plate103 rotates and slides in the direction to press the friction plates 104against the brake plates 105.

The friction plates 104 and the brake plates 105 are disposedalternately behind the pressure plate 103. The peripheral portions ofthe friction plates 104 engage with the transmission casing 107, and thebrake plates 105 with the output shaft 102.

The friction plates 104 are not rotatable relative to the transmissioncasing 107 but are slidable in the longitudinal direction of thetransmission casing 107. On the other hand, the brake plates 105 are notrotatable relative to the output shaft 102 but are slidable in thelongitudinal direction of the transmission casing 107.

The friction plates 104 and the brake plates 105 are disposed betweenthe pressure plate 103 and a rib of the transmission casing 107. Bysliding the pressure plate 103 backward with respect to the transmissioncasing 107, the friction plates 104 are pressed against the brake plates105, thereby generating force for braking the output shaft 102.

Accordingly, the braking force is applied on the output shaft 102 so asto actuate as a parking brake.

Since the brake mechanism 74 is disposed in the traveling power take-offsection, i.e., the lower portion of the rear transmission casing 5, thedistance between the brake pedal 54 and the brake mechanism 74 is soshort as to provide a compact linkage therebetween facilitating for itssimple design and operativity.

Next, description will be given of a frame construction of the crawlertractor in accordance with FIGS. 7 and 8.

The main frames 6 are disposed in the front portion of the vehicle body,and the engine 3 is disposed on the main frames 6. The HST for turning20 is disposed between the main frames 6. The front transmission casing16 is connected to the main frames 6, and the drive sprockets 11 aredisposed on outsides of the front transmission casing 16.

The front ends of the crawler frames 15 are connected to the outersurfaces of the front transmission casing 16. The crawler frames 15 arealso connected to the clutch casing 19 with frames 254 through supportframes 251. Furthermore, the rear ends of the crawler frames 15 areconnected to the rear transmission casing 5 through rear support frames252.

The frames 254 cover the left and right sides of the HST for traveling22 and the transmission shaft 45. Side frames 253 are disposed on therespective outer surfaces of the frames 254, and connect the supportframes 251 with the rear support frames 252.

Next, description will be given of the construction of the frames 254according to FIGS. 9 to 11.

The frames 254, which are C-like shaped when viewed in front, connectthe clutch casing 19 and the rear transmission casing 5 to each other.As the above mentioned, the engine 3 is laid on the main frames 6, andthe clutch casing 19 is attached to the rear portion of the engine 3.

The frames 254 are connected to the left and right surfaces of theclutch casing 19, and the rear transmission casing 5 is connected to therear portions of the frames 254.

Since the frames 254 connect the clutch housing 19 and the reartransmission casing 5 on their left and right sides, the engine 3 isintegrated with the rear transmission casing 5 through the frames 254.

Due to the above-mentioned frame construction, the HST for traveling 22is provided with a vertical opening which is advantageous formaintainability and cooling effect. For example, with regard to thisembodiment, by removing a cover of a floor step in the cabin, the HSTfor traveling 22 can be maintained from its upper side. Since the frames254 is clamped to the rear transmission casing 5 and the clutch casing19 with bolts, the frames 254 can be removed easily by removing thebolts.

Further, this frame construction has sufficient strength against torsionand vertical weighting in spite of its lightweight.

Furthermore, as an embodiment shown in FIGS. 12 and 13, the frames 254may be connected at the rear portions thereof to the respective crawlerframes 15 through center support frames 255, thereby enhancing framerigidity of the crawler tractor.

With regard to this embodiment, the support frame 251, the centersupport frame 255 and the rear support frame 252 are arranged atsubstantially regular intervals so as to enhance their rigidity forsupporting the crawler frame 15.

Next, description will be given of a construction for holding the toplink in the linkage 10 for lifting a working machine in accordance withFIGS. 14 to 16.

The top link 261 is rotatably supported above the rear portion of therear transmission casing 5 so that the rear end of the top link 261 isvertically rotatable. A stopper 264 is disposed above the supportedportion of the top link 261, and a hook 263 is rotatably supported on aside surface of the stopper 264. The hook 263 is open upwardly backward.

A handle 262 is disposed on the upper surface of the top link 261, andis longitudinally rotatable relative to the top link 261.

When a work machine is removed from the linkage 10, the top link 261 israised to be held.

The handle 26 is hooked on the hook 263 for holding the raised top link261. Namely, the top link 261 is rotated upwardly, and then the handle262 is pushed down ahead and engaged with the hook 263.

At this time, a rotation fulcrum 263 b of the hook 263, a rotationfulcrum 262 b of the handle 262, and a point 265 where the handle 262 isengaged with the hook 263 are aligned on a straight line. Also, therotational axis of the hook 263 and the rotational axis of the handle263 are parallel.

Accordingly, when the top link 261 is rotated vertically by a shock intraveling of the vehicle or another, the hook 263 and the handle 262 arerotated, and the line, which passes along the rotation fulcrum 263 b,the engaging point 265 and the rotation fulcrum 262 b, is bent. Namely,the shock is absorbed and distributed by rotation of the handle 262 andthe hook 263.

Since the hook 263 is provided in the vicinity of the stopper 264, therotational degree of the hook 264 is restricted by the stopper 264.Accordingly, the top link 261 is prevented from interfering withcircumferential parts and being damaged. Furthermore, since a portion ofthe stopper 263 for abutting against the hook 264 is disposed above thehook 264, parts disposed above the stopper 264 are protected from thehook 263.

When the handle 262 is going to be removed from the hook 263, the toplink 261 is rotated upwardly so that the hook 263 abuts against thestopper 264. Then, by rotating the top link 261 further upwardly, thehandle 262 is slid forwardly against the hook 263. Accordingly, thehandle 262 is disengaged from the hook 263.

Then, the hook 263 is rotated downwardly, and the handle 262 is pusheddown rearwardly. The top link 261 is moved down so as to be releasedfrom its held state.

A disc spring or the like is disposed on the rotational axis of the hook263 so as to press the hook 263 perpendicularly to the rotationaldirection of the hook 263, so as to generate friction force for holdingthe rotated hook 263 at the place.

Therefore, even if the top link 261 is rotated upwardly by a shock intraveling of the vehicle or another and the hook 263 is disengaged fromthe handle 262, the hook 263 is held in its upwardly rotated place.Accordingly, when the top link 261 is rotated downwardly, the hook 263and the handle 262 are engaged again.

Namely, unless the hook 263 is rotated downwardly, the engaging state ofthe top link 261 is sustained.

Next, description will be given of hydraulic piping construction inaccordance with FIGS. 17 to 20.

The crawler tractor is provided with a hydraulic pump for supplyingpressure oil to the working machine connected to the front or rearportion of the vehicle body. Pressure oil is supplied from the hydraulicpump to front and rear connection ports (specifically, a front hydraulicport 285, and couplers 275 and 276) through a sub control valve(hereafter, referred to as a SCV) 277.

The SCV 277 is disposed sidewise from the rear transmission casing 5.With regard to this embodiment, there are two hydraulic systems directlycontrolled by the SCV 277. The systems are a first system 400 comprisingpipings 280 and 281, and a second system 401 comprising pipings 282 and283.

As shown in FIG. 20, the first system 400 is connected to anelectromagnetic switching valve 278, and is constructed so as toselectively supply pressure oil to either a front first system 402 or arear first system 403. The front first system 402 comprises pipings 271and 272. The front first system 402 is connected at one end thereof tothe electromagnetic switching valve 278, and at the other end thereof tothe front hydraulic port 285. The rear first system 403 comprisespipings 406 and 407. The rear first system 403 is connected at one endthereof to the electromagnetic switching valve 278, and at the other endthereof to the coupler 275.

According to the above construction, two hydraulic systems: one for afront-loaded working machine; and the other for a rear-loaded workingmachine, are selectively controlled by operation of the SCV 277 forpressure oil supply to the first system 400 combined with switchingoperation of the electromagnetic switching valve 278.

On the other hand, the hydraulic route construction on the downstream ofthe second system 401 is substantially similar with the hydrauliccircuit construction on the downstream of the above-mentioned firstsystem 400.

The second system 401 is connected to an electromagnetic switching valve279, and is constructed so as to selectively supply pressure oil toeither a front second system 404 or a rear second system 405. The frontsecond system 404 comprises pipings 273 and 274. The front second system404 is connected at one end thereof to the electromagnetic switchingvalve 279, and at the other end thereof to a front hydraulic port 285.The rear second system 405 comprises pipings 408 and 409. The rearsecond system 405 is connected at one end thereof to the electromagneticswitching valve 279, and at the other end thereof to the coupler 276.

According to the above construction, two hydraulic systems: one for afront-loaded working machine; and the other for a rear-loaded workingmachine, are selectively controlled by operation of the SVC 277 forpressure oil supply to the second system 401 combined with switchingoperation of the electromagnetic switching valve 279.

Namely, the maximum number of controllable hydraulic circuit systems byoperative combination of the SCV 277 with the electromagnetic switchingvalves 278 and 279 is four, that is, the maximum two systems for a frontworking machine and the maximum two systems for a rear working machine.

In this embodiment, the two electromagnetic switching valves 278 and 279are provided on the downstream of the SCV 277. Alternatively, such anelectromagnetic switching valve may be added so as to increase thenumber of controllable hydraulic systems by the single SCV 277.

Next, description will be given of an arrangement of a fuel tank and anoil tank in accordance with FIGS. 21 and 22.

Rear fenders 203 are disposed on left and right sides of the lower rearportion of the cabin 9 so as to cover the lower rear side of the cabin9. A fuel tank 192 is disposed in the left rear fender 203. A pressureoil tank 215 for HST is disposed in the right rear fender 203. An oilcooler 195 is disposed in front of the pressure oil tank 215.

A refueling opening of the fuel tank 192 is disposed outward forfacilitating fuel-supply to the fuel tank 192.

An auxiliary base on which an oil feeding tank and others are mountedwill be described in accordance with FIGS. 23 and 24.

An auxiliary base 197 is disposed in the lower portion of the fender 203with the fuel tank 192 therein. The auxiliary base 197 is horizontallyrotatably supported at a front portion thereof on a pivot 199. A releaselever 198 is attached to the rear portion of the auxiliary base 197, andis engaged with the auxiliary base 197 when the auxiliary base 197 isstored.

A hook is provided on the release lever 198. The hook is engaged with astopper 196 fixed to the vehicle body so as to keep the auxiliary base197 in the stored state.

When the auxiliary base 197 is going to be used, the lever 198 is pulledso as to disengage the hook from the stopper 196. Then, the auxiliarybase 197 is pulled out rotating around the pivot 199.

Since the auxiliary base 197 receives frictional force only from thepivot 199, it can be pulled out smoothly. Accordingly, expansion of theauxiliary base 197 can be done easily. Furthermore, the auxiliary base197 may be constructed compact.

A refueling opening 201 is provided in the upper portion of the fender203 on the left side of the vehicle body, and fuel is supplied to thefuel tank 192 through the refueling opening 201. The auxiliary base 197is disposed rearward from the refueling opening 201 so that the frontportion of the auxiliary base 197 is disposed in the vicinity of therefueling opening 201 in the longitudinal direction.

Accordingly, as shown in FIG. 23, when an oil-feeding tank 200 is placedon the auxiliary base 197, an opening of the oil-feeding tank 200 ispositioned in the vicinity of the refueling opening 201 so as to beeasily inserted into the refueling opening 201.

Next, description will be given of the construction of hydrauliccircuits of the crawler tractor in accordance with FIGS. 25 to 27.

Hydraulic circuits of the crawler tractor are broadly divided into twocircuits. One is a circuit for driving the transmission and the workingmachine, and controlling the attitude of the crawler tractor. The otheris a circuit for actuating the HST for turning 20 and the HST fortravelling 22. Hydraulic pumps 182 and 191 for supplying pressure oil(lubricating oil) to these hydraulic circuits are actuated by drivingforce of the engine 3.

Pressure oil (lubricating oil) drawn up by the hydraulic pump 191 fromthe bottom of the rear transmission casing 5 through a piping 363, afilter 364 and a piping 365 is supplied to a clutch actuation circuit ofa transmission 204 in the rear transmission casing 5 through a piping366, and further supplied to a flow dividing valve 208. A level controlmechanism 205 and a lift control mechanism 207 are connected to the flowdividing valve 208 so as to be supplied with pressure oil therefrom. Alift actuating mechanism 206 and the oil cooler 195 are connected to thedownstream of the lift control mechanism 207 so as to be supplied withpressure oil. Pressure oil cooled by the oil cooler 195 is returned tothe rear transmission casing 5.

On the other hand, pressure oil drawn up by the hydraulic pump 182 fromthe pressure oil tank 215 through a piping 370, a filter 371 and apiping 372 is branched at a branch point 216 through a piping 374 and afilter 375. A part of the pressure oil is supplied from the branch point216 to the HST for traveling 22 through a piping 376. Return pressureoil of the HST for traveling 22 is returned to the pressure oil tank 215through a common returning piping 212.

The remainder of the pressure oil is supplied from the branch point 216to the HST for turning 20 through a piping 377. Return pressure oil ofthe HST for turning 20 is cooled by an oil cooler 214 provided in thefront portion of the crawler tractor, and then is returned to thepressure oil tank 215 through a piping 378 and the common returningpiping 212.

According to this construction, it is not necessary to provide separateoil coolers for cooling the HST for turning 20 and the HST for traveling22, thereby reducing weight of the crawler tractor. Also, the oilpassages is constructed so simply as to reduce cost of the crawlertractor.

A bypass switch 209 comprising relief valves and others is provided in areturn pressure oil passage from the HST for turning 20 in parallel tothe oil cooler 214.

The circuit through the bypass switch 209 bypasses the oil cooler 214.If the oil cooler 214 is clogged, the flux of pressure oil supplied tothe HST for turning 20 is reduced so as to spoil a good performance ofthe crawler tractor in turning. Therefore, in the case that the oilcooler 214 is clogged or pressure oil have such low temperature as torequire no further cooling, pressure oil is returned to the pressure oiltank 215 through the bypass circuit bypassing the oil cooler 214,thereby constantly keeping the good performance of the crawler tractorin turning.

Using the clogging oil cooler 214 for a long time is not desirable inthe viewpoint of durability of the HST for turning 20 and the HST fortraveling 22. Therefore, a sensor or the like is preferably provided tothe bypass switch 209 so as to easily detect the condition of the bypassswitch 209.

With regard to this embodiment, the oil cooler 214 is arranged in thefront portion of the crawler tractor, and the oil cooler 195 is arrangedin the rear fender 203 disposed in the rear portion of the crawlertractor, but the construction is in no way limited to this. They may beinterchanged or changed in location in consideration of heat radiatedtherefrom when they are cooled.

A construction in the vicinity of the oil cooler 214 of this embodimentwill be described in accordance with FIGS. 28 to 31.

A capacitor for air-conditioner 124 is disposed behind the oil cooler214, and a radiator 125 is disposed behind the capacitor forair-conditioner 124.

A fan (not shown) is disposed behind the radiator 125 so as to take inair from the front and exhaust it to back.

A seal member 126 is equipped between the radiator 125 and the capacitorfor air-conditioner 124. The seal member 126 is equipped on thecircumferential portion of the radiator 125 and abuts against thecircumferential portion of the capacitor for air-conditioner 124.Accordingly, the capacitor for air-conditioner 124 is sealed with thecontact portion of the radiator 125 so as to prevent air between theradiator 125 and the capacitor for air-conditioner 124 from flowing out,so that quantity of air flowing into the capacitor for air-conditioner124 is increased to enhance cooling efficiency of the capacitor forair-conditioner 124.

The seal member 126 comprises a tubular contact portion 126 b and asectionally C-like attached portion 126 c. Accordingly, the contactportion 126 b is easily deformable when pushed, and has high adherence.The seal member 126 may be made of elastic material such as gum so as tofacilitate for attachment and detachment of the attached portion 126 c.Easy removable weather strip may be used as the seal member 126.

As mentioned above, the seal member 126 enhances adherence of theradiator 125 with the capacitor for air-conditioner 124. The long-termused seal member 126 is easily detached so that dust may be easilycleared out therefrom. Accordingly, the maintainability is improved,overheat is prevented, and lives of the parts are prolonged.

Next, description will be given of arrangement of the oil cooler 195 ofthis embodiment.

As mentioned above, the oil cooler 195 is disposed in front of thepressure oil tank 215, in the rear fender 203. Since the lower portionof the rear fender 203 is opened, airflow is generated in the rearfender 203 by the movement of the crawler so as to prevent thetemperature therein from easily arising. Since the oil cooler 195 isdisposed in the lower portion of the rear fender 203, air is suppliedfrom the outside to the oil cooler 195. The pressure oil tank 215arranged in front of the oil cooler 195 protects the oil cooler 195 fromsplashes of mud.

An electric fan attached to the oil cooler 195 takes in the air fromoutside of the vehicle body, and exhausts it into the inside of thevehicle body, thereby preventing noise of the fan from easily leakingout.

A switch is disposed in the transmission casing so as to control thefan. The switch is turned on when oil temperature rises, and turned offwhen oil temperature falls.

Since the oil cooler 195 is disposed near the rear transmission casing 5so as to facilitate for shortening pipings thereto and for its compactdesign.

The oil cooler 195 arranged as mentioned above has enhanced coolingeffect so as to improve durability of the fan of the oil cooler 195 andsave energy required for its cooling. The rear fender 203 covering theoil cooler 195 and the pressure oil tank 215 keeps good appearance andreduces noise.

A sufficiently large space is ensured in the rear fender 203 so as toenhance the flexibility of arrangement of the oil cooler 195.Accordingly, as shown in FIG. 31, the air-exhaust side of the oil cooler195 is directed to the pressure oil tank 215.

By directing the air exhausted from the oil cooler 195 to the pressureoil tank 215, the pressure oil tank 215 is cooled by the exhausted air.

Description will now be given on the connection construction between theHST for turning and the front transmission casing according to FIGS. 32to 34.

The engine 3 is laid on the main frames 6. An input shaft 221 of thefront transmission casing 16 is disposed in front of the engine 3. TheHST for turning 20 is disposed in front of the front transmission casing16.

Driving force of the engine 3 is inputted into the front transmissioncasing 16 through the input shaft 221, and transferred to thedifferential gear mechanism in the front transmission casing 16 againthrough the HST for turning 20.

The driving force inputted to the input shaft 221 is transmitted to aninput shaft 222 of the HST for turning 20 through the transmission inthe front transmission casing 16. The input shaft 222 drives a hydraulicpump of the HST for turning 20, and an output shaft 223 is driven by ahydraulic motor of the HST for turning 20.

The output shaft 223 of the HST for turning 20 is connected to thedifferential transmission shaft 224, which transfers driving force tothe left and right planetary gear mechanisms 340L and 340R constitutingthe differential gear unit in the front transmission casing 16.

Spline grooves are formed on the rear end of the output shaft 223 andthe front end of the differential transmission shaft 224, so that a boss225 may be fitted on the output shaft 223 and the differentialtransmission shaft 224.

The boss 225 is slidable longitudinally on the rear end of the outputshaft 223 and the front end of the differential transmission shaft 224.In the case that the boss 225 is engaged with both the output shaft 223and the differential transmission shaft 224, driving force of the outputshaft 223 is transferred to the differential transmission shaft 224. Inthe state that the boss 225 is engaged with only the differentialtransmission shaft 224, output of the output shaft 223 is nottransferred to the differential transmission shaft 224.

On the rear peripheral portion of the boss 225 is formed a recess 226. Afork 227 fixed to a piston 228 is engaged at one end thereof in therecess 226.

The piston 228 is disposed in the longitudinal direction of the vehiclebody, and inserted at one end thereof into a cylinder part 230 providedin the front transmission casing 16. A spring is engaged with the piston228, and abuts against the fork 227 and the front transmission casing 16so as to bias the piston 228 forward.

The piston 228 is inserted at a front end thereof into the cylinder part230, to which an oil passage 229 is connected, so that charge pressureis transferred to the cylinder part 230 through the oil passage 229.

When oil pressure in the cylinder part 230 increases and the forceapplied to the piston 228 becomes larger than the bias force of thespring, the piston is slid backward. Then, the fork 227 connected to thepiston 228 makes the boss 225 slide backward, thereby shutting off thetransfer of driving force from the output shaft 223 to the differentialtransmission shaft 224.

When oil pressure in the cylinder part 230 decreases, the fork 227connected to the piston 228 makes the boss 225 slide forward, therebytransferring driving force from the output shaft 223 to the differentialtransmission shaft 224.

Since the clutch mechanism which performs on-off operation of transferof driving force is provided between the HST for turning 20 and theactuation mechanism, and the fork connected to the clutch is slid by oilpressure, the on-off operation of driving force of the HST for turning20 can be performed with simple construction. Furthermore, since thefork 227 is slid by the piston using charge pressure, the slidemechanism for the fork can be constructed easily. In addition, chargepressure can be used easily by connecting the hydraulic passage 229 to ahydraulic circuit supplied with charge pressure.

Next, description will be given of the construction for driving a frontPTO shaft.

As shown in FIGS. 35 and 36, the input shaft 222 of the HST for turning20 is inserted into a pulley 232 so that the pulley 232 is rotatedintegrally with the input shaft 222. A casing of the HST for turning 20is projected in the extension direction of the input shaft 222 aroundthe input shaft 222. The pulley 232 is fitted to the projecting part ofthe casing of the HST for turning 20 through a bearing. Namely, thepulley 232 is supported by the casing of the HST for turning 20 so asnot to stress the input shaft 222.

A belt 237 is looped over the pulley 232 so as to transfer driving forceof the pulley 232 to a front PTO mechanism 234. In the front PTOmechanism 234, the belt 237 is looped over a pulley 235. The pulley 235is connected to a front PTO shaft 236 so as to construct the front PTOshaft 236 to be rotated integrally with the pulley 235. The constructionfor transferring driving force to the front PTO mechanism 234 throughthe belt 237 is simple, and flexibility of its design is improved.

The front PTO mechanism 234 is arranged under the input shaft 222 so asto bypass the frames 6, thereby being connected to the PTO shaft 236.

In this regard, the input shaft 222 of the HST for turning 20 projectsso as to be attached to the pulley 232, thereby taking off power fordriving a working machine equipped on a front portion of the workingvehicle.

According to the above-mentioned construction, a PTO section with asimple construction is provided at the front portion of the vehiclebody, thereby facilitating maintainability and assembly thereof.

Next, description will be given of operative construction for turning,main speed change, and brake.

Referring to FIG. 37, the steering wheel 7 is connected to a steeringbox 52, so that operation of the steering wheel 7 is transferred to aconic linkage 53 through the steering box 52. Also, a main speed changelever 55 is connected to the conic linkage 53 through another linkage. Abrake pedal 54 is disposed in the vicinity of the conic linkage 53.

Operation of the steering wheel 7 and operation of the main speed changelever 55 are inputted into the conic linkage 53.

In the conic linkage 53, joint portions are moved along a bottom surfaceand side surfaces of conic shapes.

A rod for straight traveling and a rod for turning are located at oneends thereof to serve as respective peaks of two large and small conicshapes while they are located at the other ends thereof on the commonbottom circle of the conic shapes with the phase difference of 90degrees. Therefore, the peaks of the conic shapes for straight travelingand for turning are moved in association with location of arms foroperating the HST for traveling 22 and the HST for turning 20.

It is constructed so that the rotational angle of the main speed changelever 55 is proportional to the inclination of the bottom surface of theconic shapes and the rotational angle of the steering wheel 7 isproportional to the rotational angle of the bottom surface of the conicshapes.

In a stationary state, even if the steering wheel 7 is rotated left orright, constant distances from the peaks to the bottom circle of theconic shapes are kept so as to prevent the operation arms of the HST fortraveling 22 and the HST for turning 20 from moving. Accordingly, thehydraulic motors of the HST for traveling 22 and the HST for turning 20are not driven, so that the vehicle remains stationary.

Next, when the main speed change lever 55 is pushed down to itsadvancing direction, the operation arm of the HST for traveling isrotated to its advancing side. However, since the end of the rod forturning is located on the rotational center line of the bottom surfaceof the conic shape, the operation arm of the HST for turning 20 remainsstationary regardless of the inclination of the bottom surface, wherebythe vehicle travels straight.

If the steering wheel 7 is turned from this state, the operation arm ofthe HST for traveling 22 is moved to its slowing down direction, and theoperation arm of the HST for turning 20 is moved. Namely, as thesteering wheel 7 is turned, the crawler tractor turns while beingautomatically decelerated.

In the backing state, when the steering wheel 7 is turned, the operationarm of the HST for turning 20 is moved to the direction opposite to thatin advancing. The operation of the HST for turning 20 is reverseddepending on whether it is done in advancing or backing, therebycanceling the reverse steering phenomenon.

As mentioned above, operation of the steering wheel 7 and operation ofthe main speed change lever 55 are linked mutually by the conic linkage53. In this embodiment, furthermore, operation of the brake pedal 54 islinked with operation of the main speed change lever 55 or rotation ofthe operation arm of the HST for traveling 22.

Description will now be given of the conic linkage 53 according to FIGS.38 and 39.

A steering input shaft 112 is connected to the above-mentioned steeringwheel 7 through a universal joint, so that the steering input shaft 112is connected at a lower end thereof through the universal joint to arocking member 117 of a converting mechanism for bringing the turningdirection of the vehicle into correspondence to speed change inadvancing and backing.

The rocking member 117 is formed in a substantially conic shape, and issupported at a middle portion thereof by a bracket provided on an end ofa rocking shaft 118 through a bearing. The rocking member 117 is rotatedaround the steering input shaft 112 and tilted around the rocking shaft118 in connection with the rotation of the above-mentioned steeringwheel 7. The rocking shaft 118 is rotatably supported by an innersurface of a column through a bearing so as to arrange the axis of therocking shaft 118 laterally horizontally.

An arm part 133 is extended laterally from the rocking member 117 so asto be connected at an end thereof to a connection member 119. A steeringlink 115 is connected to one end of the connection member 119 through auniversal joint or the like, and a traveling link 111 is connected tothe other end of the connection member 119 through a joint.

When the steering wheel 7 is positioned in its straight travelingposition, the joint for connecting the steering link 115 with theconnection member 119 is positioned on extension of the axial center ofa bracket provided on an end of the above-mentioned rocking member 117.The rocking shaft 118 is arranged in the lateral direction to intersectextension of the above-mentioned axial center of the bracket when it isset in neutral.

Also, the steering link 115 is connected at a lower end thereof to anarm engaged with a shaft 89, so that, by rotating the arm, a rod 106 isoperated so as to operate the speed change arm of the HST for turning20.

The travel link 111 is connected to the other end of the connectionmember 119 disposed on the rocking member 117 through a joint. Thisjoint is arranged in the position at an angle of 90 degrees from theabove-mentioned joint connecting the steering link 115 with theconnection member 119 with respect to the axial center of the bracket147 on the end of the above-mentioned rocking member 117.

Then, the lower end of the travel link 111 is connected to an armengaging at one end thereof with a shaft 116. A rod 127 is connected atone end thereof to an arm connected to the shaft 116, and at the otherend thereof to one end of an arm fitted on the shaft 89.

The lower end of the above-mentioned steering link 115 and the lower endof the travel link 111 are arranged on extension of the axial center ofthe bracket 147 on the end of the rocking member 117.

An arm 120 is projected backward from the bracket 147 of theabove-mentioned rocking shaft 118. A main speed change link 114 isconnected at an upper end thereof to an end of the arm 120, and at alower end thereof to the arm engaged on the shaft 89. Accordingly, themain speed change link 114 is connected to the HST for traveling 22.

Next, description will be given of a linkage of the main speed changelever 55 according to FIG. 40.

The main speed change lever 55 is rotatably pivotally provided at alower end thereof on a pivot 90, and a forwardly projecting arm is fixedto the lower end of the main speed change lever 55. The arm is connectedat an end thereof with an upper end of a rod 81. The rod 81 is connectedat a lower end thereof with an arm rotatably supported on a shaft 82.

The arm supported by the shaft 82 is rotated integrally with an arm 83.Accordingly, by rotating the main speed lever 55, the arm 83 is rotatedlongitudinally.

A rod 91 is connected at a rear end thereof to the lower end of the arm83, and at a front end thereof to an arm 84 fixed to the shaft 89. Thearm 84 is rotatable longitudinally around the shaft 89, and is rotatedintegrally with an arm 84 b whose one end is engaged on the shaft 89similarly. An arm 85 is connected to the arm 84 b. The shaft 89 isconnected to the above-mentioned conic linkage 53.

The rod 85 connects an arm 86 with the arm 84 b, so that the arm 86 isrotatably supported at the lower end thereof. A plate 87 is disposedlongitudinally and is connected to the arm 86. An arm 88 of the HST 22is connected to an end of the plate 87.

Due to such a linkage, the HST for traveling 22 is operated by operatingthe main speed change lever 55.

Next, description will be given of a linkage mechanism of the brakeaccording to FIGS. 41 and 42.

The brake pedal 54 is connected to the above-mentioned brake mechanism74 through a linkage so that the brake mechanism 74 is operated by thebrake pedal 54, whereby a parking brake is actuated.

The brake pedal 54 is fixed on a pivot 62, and the pivot 62 is rotatablysupported on an upper portion of a front column. The pivot 62 isconstructed to be rotated together with the brake pedal 54 by depressingthe brake pedal 54. Arms 63 and 64 are fixed to the pivot 62, and rods65 and 66 are fixed to ends of the arms 63 and 64, respectively.

The rods 65 and 66 are disposed longitudinally, and a cam lever 61 isconnected to the lower end of the rod 66. The cam lever 61 is rotatablysupported on a pivot fixed on a side surface of a box which contains theconic linkage 53, and is rotated by vertical sliding of the rod 66.

An arm 68 is connected to a lower end of the above-mentioned rod 65, andthe arm 68 is rotatably supported on a pivot 67. An arm 69 rotatedintegrally with the arm 68 is fixed on the arm 68, and a rod 70 isconnected to an end of the arm 69.

The rod 70 is disposed in the longitudinal direction of the vehiclebody, and an L-like shaped arm 72 rotatably supported on a pivot 71 isconnected at one end thereof to the rear end of the rod 70.

A vertical rod 73 is connected to the other end of the L-like shaped arm72, and an actuation arm 113 of the brake mechanism 74 is connected tothe lower end of the rod 73.

Accordingly, by depressing the brake pedal 54, the actuation arm 113 isrotated, thereby actuating the brake mechanism 74.

At this time, since the brake mechanism 74 is located near the brakepedal 54 (namely, around the output shaft 102 projected from the reartransmission casing 5 under the cabin 9), the link for the brake isshortened in its full length. As a result, the linkage mechanism of thebrake mechanism 74 may be designed simply, and operativity of the brakemechanism 74 is improved.

In addition, a parking brake lever 75 is provided on the inside of thebrake pedal 54 so as to anchor the depressed brake pedal 54 (in thestate for applying brake).

By depressing the brake pedal 54 and rotating the parking brake lever 75upward, the brake pedal 54 is kept in its depressed state, therebyapplying the parking brake. The parking brake is released by rotatingthe parking brake lever 75 downward.

Next, description will be given of the linkage between the brake pedal54 and the main speed change lever 55 according to FIG. 40.

As mentioned above, the shaft 89 connected to the conic linkage 53 isrotated integrally with the main speed change lever 55. An arm 92 isfixed at one end thereof to the shaft 89. By rotating the main speedchange lever 55, the arm 92 is rotated, and in connection with it, themain speed change lever 55 is rotated.

A projection 93 is provided on a tip of the arm 92 so as to project inthe direction of the rotational axis of the arm 92.

The projection 93 is positioned on the inside of a cam part of theabove-mentioned cam lever 61 so that the projection 93 may abut againstthe inner surface of the cam part of the cam lever 61 by rotating thecam lever 61.

By depressing the brake pedal 54, the cam lever 61 is rotated, and thearm 92 is returned to its predetermined position by the cam lever 61.The predetermined position where the arm 92 is returned by the cam lever61 corresponds to the neutral position of the main speed change lever55. Therefore, by depressing the brake pedal 54, the main speed changelever 55 is returned to its neutral position, and the brake mechanism 74is actuated.

For stopping a crawler tractor without applying too much load ontodriving parts and brakes, it is desirable that a main speed change leveris moved to its neutral position and then the brake is actuated.However, according to this embodiment, by only depressing the brakingpedal 54, the HST for traveling 22 returns to its neutral position andthe brake mechanism 74 is actuated.

Also, both braking force of the HST for traveling 22 (engine brake) andbraking force of the brake mechanism 74 are available as braking forcefor stopping the vehicle. The brake mechanism 74 is so constructed as toapply braking force after the HST for traveling 22 is braked, therebybeing smaller than the conventional brake mechanism.

Furthermore, by adjusting actuation timings of the two brakes, abrasionof the parking brake in the brake mechanism 74 can be prevented.

The shaft 89 is connected to the main speed change link 114 and thesteering rod 115 in the conic linkage 53, as shown in FIGS. 39 and 41.The shaft 89 is a member to which main speed change operation andsteering operation are transferred. A mechanism for keeping the HST forturning 20 and the HST for traveling 22 in neutral is provided on theshaft 89. Namely, by returning an arm connected to the shaft 89 to itsneutral position, the conic linkage 53 is returned to its neutralposition.

Also, as shown in FIG. 43, a mechanism for neutral-setting of theoperation linkage comprising the cam lever 61 and the arm 92 is arrangedin a lower portion of a chamber containing the conic linkage 53, and ispositioned in the middle of the linkage connecting the main speed changelever 55 with the steering wheel 7. Accordingly, the main speed changelever 55 can be connected with the steering wheel 7 easily, and plays ofthe main speed change lever 55 and the steering wheel 7 can be adjustedeasily.

More detailed description will be given of the mechanism forneutral-setting of the operation linkage comprising the cam lever 61 andthe arm 92 according to FIGS. 44 and 45.

The cam lever 61 is formed in a hook-like shape, and a cam is formed inthe hook. The cam shape formed in the cam lever 61 is broad in its lowerportion and narrow in its upper portion.

FIG. 44( a) illustrates the cam lever 61 and the arm 92 in the neutralstate of the brake pedal 54; FIG. 44( b) illustrates the same in thestate that the brake pedal is depressed half, and FIG. 44( c)illustrates the same in the state that the parking brake is applied.

As shown in FIG. 44( a), when the brake pedal 54 is in its neutralstate, the projection 93 does not abut against the cam lever 61, so thatthe arm 92 is free from motion of the cam lever 61. Accordingly, theactuation state of the conic linkage 53 is not restricted.

Then, as shown in FIG. 44( b), when the brake pedal 54 is depressedhalf, the arm 92 is returned to its neutral position according to thecam shape of the cam lever 61, and the conic linkage 53 is also put intoits neutral state. However, at this time, the brake mechanism 74 as theparking brake remains actuation-free.

By further depressing the brake pedal 54, as shown in FIG. 44( c), thebrake mechanism 74 actuates.

A portion of cam groove in the cam lever 61 for neutral location of thearm 92 is elongated so that the brake pedal 54 can be depressed whilethe projection 93 is located in its neutral position.

Next, description will be given of a construction of the rod 73 forconnecting the brake mechanism 74 with the brake pedal 54.

By depressing the brake pedal 54, the rod 65 is slid upward so as torotate the arms 68 and 69. Accordingly, the rod 70 is slid forwardly soas to rotate the arm 72 and slide the rod 73 upward.

A shock absorbing mechanism 73 b is provided on the rod 73. The shockabsorbing mechanism 73 b is constructed by connecting upper and lowerportions of the rod 73 through an elastic member such as a spring.According to an example shown in FIG. 45, a spring is wound around alower portion of the rod 73, and a spring is inserted into an uppercylindrical portion the rod 73.

The springs are contracted when the upper portion of the rod 73 is slidupward. When contraction of the springs reaches a fixed degree, thelower portion of the rod 73 is raised upward, thereby actuating thebraking mechanism 74.

Accordingly, the brake is actuated after the conic linkage 53 isreturned to neutral, so that load applied to the brake mechanism 74 isreduced, thereby improving the durability of the brake mechanism 74.

Since the shock absorbing mechanism 73 b is provided on the rod 73, whenthe actuation arm 113 of the brake mechanism 74 are raised upwardcompletely, the brake mechanism 74 can be actuated by a substantiallyconstant force without raising the actuation arm 113 any more. Inaddition, by providing the shock absorbing mechanism 73 b on the rod 73,it is not necessary to provide another shock absorbing mechanism on therod 65 or the like, and the arm 68 and the brake pedal 54 can beconnected mutually through a simple rod.

Next, description will be given of the construction for avoiding harshbrake according to an example shown in FIG. 46.

According to the example shown in FIG. 46, a swash plate control arm ofthe HST for traveling 22 is connected to the brake pedal 54 through aservo valve 134. Accordingly, the brake works gradually when the brakepedal 54 is operated. Therefore, the operativity is improved and hardbrake is prevented.

The brake pedal 54 is connected to the arm 68 through the rod 65. Thearm 68 is rotated integrally with the arm 69 and an arm 135.

The arm 69 is connected with the brake mechanism 74 as mentioned above,and the arm 135 is connected with the arm of the HST for traveling 22through the servo valve 134. Also, the arm of the HST for traveling 22is connected to the arm 84 b, and the arm 84 b is rotated with rotationof the main speed change lever 55.

When the brake pedal 54 is depressed, the servo valve 134 is pulledforward by the arm 135. As mentioned above, the brake mechanism 74 doesnot cause braking force unless the brake pedal 54 is depressed to somedegree, and the servo valve 134 is actuated when the arm of the HST fortraveling 22 is returned to its neutral position. Accordingly, when thearm of the HST for traveling 22 is returned to its neutral positiongradually by the servo valve 134, the conic linkage 53 and the mainspeed change lever 55 are returned to their neutral positions along withthe arm.

Then, the arm of the HST for traveling 22 is set in its neutral positionso as to apply an engine brake, thereby braking the crawler tractor tosome degree, and then, the brake mechanism 74 is actuated so as to applya sure parking brake to the crawler tractor.

Accordingly, harsh brake is prevented so as to improve operativity ofthe crawler tractor.

Next, description will be given of a construction of the steering box 52according to FIGS. 47 to 50.

The steering box 52 is disposed between the steering wheel 7 and theconic linkage 53 so as to transmit operation of the steering wheel 7 tothe conic linkage 53.

A steering shaft 151 is rotatably disposed in the steering box 52, and acam box 163 is provided on the lower part of the steering box 52. Thesteering shaft 151 projects at an upper portion thereof upward from thesteering box 52 and connected to the steering wheel 7. The steeringshaft 151 projects at a lower portion of the steering shaft 151 into thecam box 163.

A gear 152 is formed on a lower end of the steering shaft 151 so as toengage with a cam gear 150.

A steering transmission shaft 164 is fixed on the rotation center of thecam gear 150, and connected at a lower end thereof to the steering inputshaft 112 of the conic linkage 53 through a universal joint or the like.

According to the above-mentioned construction, when the steering wheel 7is rotated, the steering shaft 151 is rotated, and then the steeringtransmission shaft 164 is rotated with the cam gear 150. Therefore, thesteering input shaft 112 connected to the steering transmission shaft164 is rotated.

A cam mechanism for restricting rotation of the steering wheel 7 andreturning the steering wheel 7 to the neutral position is built in thecam box 163.

A cam 153 is equipped on a lower surface of the cam gear 150 fixed tothe steering transmission shaft 164 so as to be rotated integrally withthe cam gear 150. A support base 161 is provided in the lower part ofthe cam box 163, and a stopper 156 for restricting rotation of the cam153 is provided upright on the support base 161.

A neutral return mechanism 166 is provided symmetrically with thestopper 156 with respect to the rotational center of the cam 153. Theneutral return mechanism 166 comprises a roller 157, an arm 158 and aspring for biasing the arm 158 toward the cam 153.

The arm 158 is rotatably supported at one end thereof by an uprightshaft provided on the support base 161, and the roller 157 is rotatablysupported on the arm 158. Since the arm 158 is biased toward the cam153, the roller 157 is pressed against the cam 153. The stopper 156 andthe roller 157 as a neutral returning member are disposed symmetricallywith respect to the axial center of the cam 153.

The cam 153 is provided with a contact portion 154 for abutting againstthe stopper 156 and with a neutral portion 155 for abutting against theroller 157 in neutral. The contact portion 154 is formed on a sidesurface of the cam 153 furthest apart from the rotational center of thecam 153, and the neutral portion 155 nearest to the rotational center ofthe cam 153. The contact portion 154 and the neutral portion 155 areconnected mutually through a smooth curve line, so that the cam 153 isformed symmetrically with respect to a line joining the rotationalcenter of the cam 153 and the neutral portion 155. The cam 153 is formedto gradually expand in its radial direction as it goes apart from itsneutral position, and the cam 153 is formed at one end thereof with thecontact portion 154 for abutting against the stopper for restrictingrotation thereof.

When the cam 153 constructed as mentioned above is rotated from itsneutral position, the cam 153 pushes away the roller 157 against biasingforce of the spring. Since the roller 157 is biased toward the cam 153,when the steering wheel 7 is released from an operator's hands, the cam153 is rotated so as to return to its neutral position.

The cam 153 is rotatable unless the contact portion 154 abuts againstthe stopper 156, so that rotation of the cam 153 is restricted based onthe positions of the stopper 156 and the contact portion 154.

A plate 159 is fixed at one end thereof on a lower surface of the arm158. The plate 159 is extended downward, and a bolt and a nut areequipped on the lower end of the plate 159 in the rotation direction ofthe arm 158.

A switch base 160 is attached to the support base 161 toward theabove-mentioned plate 159. On an end of the switch base 160 is disposeda switch 171, which is brought into contact with the bolt on the plate159 so as to be turned on or off.

Namely, by rotating the steering wheel 7, the cam 153 is rotated, andthe arm 153 is rotated so as to change a distance between the switch 171and the above-mentioned bolt. The distance between the switch 171 andthe bolt becomes the shortest when the cam 153 is in its neutralposition, and becomes the longest when the contact portion 154 of thecam 153 abuts against the stopper 156. According to this construction,the switch 171 detects the neutral location of the cam 153.

Next, description will be given of a mechanism for releasing residualpressure of the HST for traveling according to FIGS. 41, 42 and 51 to53.

By depressing the clutch pedal 54, as mentioned above, the arm of theHST for traveling 22 is set in its neutral position, and the brakemechanism 74 is actuated after the crawler tractor is braked to somedegree by engine brake of the neutral HST for traveling 22. At thistime, the HST for traveling 22 is stopped when one of a pair of passageswhich mutually connect a motor 22 a and a variable type pump 22 b in theHST for traveling 22 is hydraulically pressured higher than the other.Namely, each plunger of the motor 22 a and the variable type pump 22 bis stressed at one end in its sliding direction by an oil pressuredifference (residual pressure) between the above-mentioned pair ofpassages so as to cause a load at the time of starting the engine.Therefore, it is desirable to release the residual pressure in the pairof passages connecting the motor 22 a to the variable type pump 22 b(namely, to cancel the pressure difference therebetween).

When the brake pedal 54 is depressed, the arm 63 is rotated integrallywith the brake pedal 54 around the pivot 62, and the rod 65 pivotallyattached to an end of the arm 63 is moved upward. At this time, the arm68 pivotally connected at an end thereof to the lower end of the rod 65is rotated together with an arm 176 around the pivot 67, and a rod 177pivotally connected to a rear end of the arm 176 is moved downward. Bymoving the rod 177 downward, a solenoid in a residual pressure releasevalve 178 is pushed in against biasing force of the spring, so as tobring pipings 180 and 181 into mutual fluidal communication forreleasing the residual pressure.

The residual pressure release valve 178 is disposed on a rear surface ofthe clutch casing 19 and in front of the HST for traveling 22, and thepipings 180 and 181 are respectively connected to the pair of passageswhich mutually connect the motor 22 a and the variable type pump 22 b inthe HST for traveling 22.

Due to the above construction, by depressing the brake pedal 54, thepair of passages which connect the motor 22 a and the variable type pump22 b are connected mutually so as to cancel the oil pressure difference(release the residual pressure). When the depressed brake pedal 54 isreleased, the above-mentioned members from the brake pedal 54 to thesolenoid in the residual pressure release valve 178 are operated in theopposite direction so as to cut off the connection of the pipings 180and 181 for releasing residual pressure, so that the main circuit of theHST for traveling 22 may be actuated.

Next, description will be given of another valve for releasing theresidual pressure.

With regard to an example shown in FIG. 53, an electromagnetic valve 188serving as a residual pressure release valve is operated by the brakepedal 54.

A linkage 184 is connected to the brake pedal 54 so as to put on/off aswitch 185 connected to the electromagnetic valve 188. When the switch185 is turned on, the electromagnetic valve 188 is slid so as tomutually connect a pair of bypassing passages 186 and 187 connected tothe motor 22 a and the variable type pump 22 b.

When the switch 185 is turned off, the electromagnetic valve 188 cutsoff the connection between the passages 186 and 187. Accordingly, whenthe brake pedal 54 is not depressed, the main circuit of the HST fortraveling 22 is not bypassed.

The linkage 184 connected to the brake pedal 54 for releasing residualpressure in the HST for traveling 22 has such a simple structure as tooperate the switch 185.

Therefore, the start of the engine is facilitated because the brakepedal is always depressed in starting operation of the engine, andresidual pressure is released with an easy construction.

Alternatively, as shown in FIG. 54, the residual pressure release valvemay be operated by a key switch.

A key switch 189 has an electric circuit, which is turned on/off by akey 190 inserted thereinto and rotated.

The electromagnetic valve 188 serving as a residual pressure releasevalve is connected to the key switch 189. The key 190 is inserted intothe key switch 189 and rotated so as to connect the key switch 189 tothe electromagnetic valve 188.

The key switch 189 serves as a starter switch of the crawler tractor, sothat, when the starter switch is actuated, the electromagnetic valve 188is operated.

Accordingly, when the starter is actuated, the pressures in the HST fortraveling 22 and the HST for turning 20 are always low so as tofacilitate for start of the engine. Also, hard actuation for releasingresidual pressure becomes unnecessary.

The above-mentioned residual pressure release valve 178, which isconnected to the main circuits of the HST for traveling 22 and the HSTfor turning 20, may be disposed in a housing integrally with the HSTs.Due to this, the residual pressure of the HST for traveling 22 and theHST for turning 20 is released so as to easily rotate the output shaftfor traveling, thereby facilitating for restarting of the engine.

INDUSTRIAL APPLICABILITY

As mentioned above, the crawler tractor according to the invention issuitable to be used as an agricultural working machine. Especially, itis usable in such a case as to travel on a muddy or hilly ground, thatis hard for a tractor having normal drive wheels to work, or as torequire a large driving force for using working machines.

1. A vehicle comprising: a hydrostatic stepless transmission fortraveling of the vehicle, the hydrostatic stepless transmission beingprovided with output control means for controlling output rotation ofthe hydrostatic stepless transmission; a speed change device foroperation of shifting the output control means; a steering device foroperation of steering the vehicle; a conic linkage linking the steeringdevice with the speed change device, the conic linkage having a rotaryportion linked to the output control means; a parking brake for brakingoutput rotation of the hydrostatic stepless transmission; a brake pedalfor controlling the parking brake; an operation link connecting thebrake pedal with the conic linkage; and a neutral return mechanism forreturning the output control means to a neutral position in response todepression of the brake pedal, the neutral return mechanism beingprovided in the operation link, the neutral return mechanism including ahook-shaped cam and an engaging member fixed on the rotary portion ofthe conic linkage, wherein, when the brake pedal is not depressed, theengaging member is disposed out of a groove of the hook-shaped cam, andwherein, by depressing the brake pedal, the hook-shaped cam rotates soas to forcibly insert the engaging member into the groove of thehook-shaped cam so as to return the rotary portion of the conic linkageand the output control means to the neutral position.
 2. The vehicleaccording to claim 1, wherein the neutral return mechanism is disposedin a lower portion of a section incorporating the conic linkage.
 3. Thevehicle according to claim 1, wherein the hook-shaped earn is arrangedon a link between the conic linkage and the speed change device.
 4. Thevehicle according to claim 1, further comprising: a residual pressurereleasing mechanism including a valve for releasing residual pressurefrom a hydraulic circuit of the hydrostatic stepless transmission. 5.The vehicle according to claim 4, wherein the residual pressurereleasing mechanism is operatively connected to the brake pedal so as toopen the valve in response to depression of the brake pedal.
 6. Thevehicle according to claim 4, wherein the valve is an electro magneticvalve, and wherein the releasing mechanism is operatively connected to akey switch so as to open the valve in response to switching the keyswitch.
 7. The vehicle according to claim 1, wherein in response todepression of the brake pedal, the parking brake begins to act forbraking after the output control means comes into the vicinity of theneutral position.
 8. The vehicle according to claim 1, furthercomprising: a servo valve interposed between the brake pedal and theoutput control means so as to gradually transmit depression of the brakepedal to the output control means.
 9. vehicle according to claim 1,further comprising: an auxiliary speed change transmission driven by thehydrostatic stepless transmission engine; a transmission casingincorporating the auxiliary speed change transmission; and a travelingpower take-off section disposed at a lower portion of the transmissioncasing so as to take off power from the auxiliary speed changetransmission, wherein the parking brake is provided in the travelingpower take-off section.
 10. The vehicle according to claim 9, furthercomprising: a differential mechanism for traveling and steering drive ofthe vehicle; and a second hydrostatic stepless transmission for steeringthe vehicle, wherein output of the traveling power take-off section andoutput of the second hydrostatic stepless transmission are combined inthe differential mechanism.
 11. A vehicle comprising: a speed changedevice for traveling speed change operation of the vehicle; a steeringdevice for steering operation of the vehicle; a conic linkage linkingthe steering device with the speed change device; a neutral-return caminterposed between the steering device and the conic linkage; aneutral-returning member moved by the neutral-return cam so as to returnthe steering device to a neutral position; and a stopper for stoppingrotation of the neutral-return cam, wherein the stopper and theneutral-returning member are arranged symmetrically with respect to arotary center axis of the neutral-return cam.
 12. The vehicle accordingto claim 11, wherein the neutral-return cam is formed with a cam portionfor abutting against the neutral-returning member and with a stoppingportion for abutting against the stopper.
 13. The vehicle according toclaim 12, wherein the cam portion of the neutral-return cam graduallyexpands in the radial direction of the neutral-return cam as the camportion shifts from a neutral position to an end, and wherein thestopping portion is provided at the radially largest end of the camportion.
 14. A vehicle comprising: a traveling hydrostatic steplesstransmission for traveling drive of the vehicle driven by engine power;a steering hydrostatic stepless transmission for steering drive of thevehicle driven by engine power; a differential mechanism including apair of differential output portions, wherein the differential mechanismhas a traveling input portion through which output rotation of thetraveling hydrostatic stepless transmission is distributed between thepair of differential output portions in the same direction and in thesame speed, wherein the differential mechanism has a steering inputportion through which output rotation of the steering hydrostaticstepless transmission is distributed between the pair of differentialoutput portions in opposite directions and in the same speed, andwherein the steering input portion is divided into coaxial first andsecond shaft portion; and a clutch interposed between the first andsecond shaft portions.
 15. A vehicle comprising: a traveling hydrostaticstepless transmission for traveling drive of the vehicle driven byengine power; a steering hydrostatic step less transmission for steeringdrive of the vehicle drive, including an input shaft for receivingengine power; a casing incorporating the steering hydrostatic steplesstransmission, wherein a part of the input shaft of the steeringhydrostatic stepless transmission projecting outward from the casing; apower take-off device; and a pulley provided on the projecting part ofthe input shaft so as to transmit power to a power take-off device.